1. Field of the Invention
The present invention relates to a vibration detection device for detecting a vibration upon photographing in an image pickup apparatus such as a camera.
2. Related Background Art
FIG. 1 shows a conventional vibration detection device of this type.
An angular velocity sensor 1 detects an angular velocity due to a vibration. A low-pass filter 2 removes high-frequency components, which are not caused by a camera shake, from the output from the angular velocity sensor 1. An amplifier 3 constitutes, using a capacitor C and resistors R, a high-pass filter for removing low-frequency components which are not caused by a camera shake, and constitutes an amplifier for non-inverting amplifying a signal from the low-pass filter 2 using an operational amplifier (denoted by OP2 in FIG. 1). A known one-chip microcomputer unit (to be abbreviated as an MCU hereinafter) 5 has an A/D conversion input. A buffer circuit 4 includes a known reference voltage generator 6. The output from the reference voltage generator 6 is supplied to the amplifier 3 via the buffer circuit 4. A start switch SW1 is connected to the MCU 5, and when the switch SW1 is turned on, the MCU 5 begins to control a series of sequences for detecting a vibration. An analogue switch SW2 is turned on/off in accordance with an output from an output port of the MCU 5. When the switch SW2 is turned on/off, the initializing operation of the amplifier 3 is controlled. The reason why the initializing operation of the amplifier 3 is performed is as follows. More specifically, since the output from the sensor varies upon power ON, a final output (V2) of the circuit also largely varies, and this variation adversely influences vibration reduction. Therefore, the initializing operation of the amplifier 3 is performed to suppress the variation. Note that this variation occurs even when the sensor generates no output.
In the prior art, the above-mentioned arrangement calculates a position corresponding to angular velocity ="0" detected by the angular sensor 1. Thereafter, upon detection of angular velocity="0", the amplifier is initialized using the analogue switch SW2. Then, vibration reduction control is executed using the output signal from the amplifier.
Note that the vibration reduction control is performed as follows. More specifically, a driving system of a partial optical system (vibration reduction optical system) in a photographing optical system is driven on the basis of the output signal from the amplifier, thereby shifting the vibration reduction optical system in a direction perpendicular to the optical axis. With this operation, image blur reduction of an object image on a film surface in the photographing optical system as a whole is achieved. The image blur reduction is known to those who are skilled in the art.
However, in the prior art, even when the angular velocity signal as an output signal from the amplifier is determined to be "0" and the initializing processing of the amplifier is performed, an error voltage is generated in the output from the amplifier 3 under the influence of an offset voltage and an input offset current of an operational amplifier OP3 constituting the buffer circuit 4, and an input offset current of the operational amplifier OP2 constituting the amplifier 3, thus often disturbing accurate vibration reduction control.